Today a large proportion of people have at least one email (electronic mail) account, and there are a variety of ways in which an individual can obtain an email account. For example, a user's employer may provide them with an email account, or when a user subscribes to an Internet Service Provider (ISP) they will usually be provided with at least one email account. In addition, a user can create an email account with one of a number of email services, such as Google's Gmail®, Microsoft's Hotmail® etc.
Each email account is associated with at least one email address that is unique to that account, and therefore allows any emails sent to this address to be delivered appropriately. Email addresses take the form “local-part@domain”, wherein the domain identifies the entity/entities that host the account associated with the email address, and the local-part identifies the individual email account to the host (see, for example, IETF RFC 5321).
When creating an email account, it is often the case that a user is free to define what the local-part of their email address will be, provided that it is unique to the host. As such, a recipient of an email cannot necessarily rely on the email address as a means for correctly identifying the sender. For example, an email sent from the email address “john.smith@emailservice.com” may not be from an individual whose name is actually John Smith. Furthermore, even if the local-part of the email address does in some way accurately represent the actual name of the sender, the recipient of the email can not be certain which particular individual the email is from. This is particularly true of those email addresses wherein the domain part of the email address identifies a host that allows anybody to create an email address.